Questions about “Brightness”, “Color Temperature”, and All That

Are the 800 Lumens 5000 K Daylight LEDs I bought for my home just as bright as the same Lumens 2700 K Soft White LEDS? 

The total light emitted by a light bulb is measured in lumens. The “color” of the light bulb is characterized by its color temperature. An 800 lumen light bulb emits the same amount of light whether it has a color temperature of 2700 K or 5000 K.  

So light that is amberish, that I think of as warm, is in fact a cooler color? I just want to use the word well.

The terminology used for describing the color of lighting is confusing.

On the one hand, when we describe a color by the mood or ambience it creates, amber is “warm” and white or blue-white is “cool”.

On the other hand, when we describe light color by temperature, amber is lower temperature than white or blue-white.

To avoid as much of this confusion as possible, when engineers and scientists are using temperature to describe lighting they avoid using terms, like warm and cool, whose meaning might be confused.

You can get an imperfect sense of the color temperature continuum from this graphic, which is posted at the city’s lighting project web site. This is not a perfectly accurate presentation – this graphic is of incandescent, and not LED, lighting – but it will enable you to get a sense of the color temperature continuum.

I would also like to hear more about scatter of light due to temperature, please.

All the light we see is a mix of the “rainbow colors”: that is, the very particular colors – tint, hue, and shade – that you see in a rainbow. You can read more about this in our section on spectra. When light that is a composite of the rainbow colors strikes air molecules, or water vapor or dust suspended in the air, the blue-indigo-violet components of the light are much more likely to “ricochet” – or scatter – off the air, water, or dust and head-off in odd directions than are the red-orange-yellow components. 

This is the reason that the sky is blue: the blue-indigo-violet contribution to the light coming from the sun are preferentially scattered by the molecules in the atmosphere. When you look away from the sun and see blue sky, what you are seeing is that ricocheted blue component of sunlight that was not initially directed toward. 

This is also the reason that a sunset or sunrise is red: at sunset, sunlight is passing through much more of Earth’s atmosphere than during mid-day; so, much more of the blue component of the sunlight is scattered away from the direct light of the sun. The light that remains thus has a much greater fraction of red light, compared to blue light, than the noon-day sun. 

The same effect is also the reason why fog lights on cars and trucks are generally amber in color: the amber light is much more penetrating – i.e., less likely to be scattered – in passing through the fog than would be light toward the bluer end of the spectrum. 

Finally, recall that the color temperature of a light describes the ratio of blue-indigo-violet to red-orange-yellow. Thus, light with a higher color temperature – a greater fraction of blue-indigo-violet light to red-orange-yellow light – is much more likely to scatter off of air molecules and lead to a sky glow or light dome over a city.  

Can you have 3,000 Kelvin amber light or does amber light have to be at a lower Kelvin?

No: there is no such thing as a 3000 K amber light.

When temperature is used to describe a light – as in a 3000 K light – it refers to the light color. Amber is the color of light the 2000 – 2200 K range. A 3000 K light is always at the high end of what is called “soft white”, tending toward “bright white” or “cool white”. [“Bright”, in this context, means bold and vivid. It does not refer to intensity of illumination.]  

Is the brightness of lower Kelvin lamps equivalent to  the brightness of of a higher Kelivn lamp?

Brightness and color temperature are entirely independent. A low color temperature (e.g., 2000 K amber) light can be bright; a high color temperature (e.g., 4000 K blue-white) light can be dim. And, vice versa. One way to keep the distinction between brightness and color temperature in mind is to imagine a collection of identical table candles. Each candle will give off light of  exactly the same color. The color of the light from two candles brought together will not be any different than the color of either candle seen individually; but, the amount to light from two, or three, or four candles candles will be two, or three, or four times as great as the light from a single candle. 

Can the LED lights have covers that make the light output appear as yellow?. And what might be the additional cost factor?

You could take a high color temperature light and add a filter that would remove the blue from the light, leaving only the red-orange-yellow. The filter would get very hot – all the blue-indigo-violet light that is filtered out would be converted into heat of the filter and the operating temperature of the enclosed LEDs. The result would also be much dimmer; so, to get the same intensity of yellow light you would need to greatly increase the brightness of the bare light. This would, in turn, greatly increase the power consumption of the light. Finally, the high operating temperature of the LEDs would shorten their lifetime and, very likely, void their warranty. 

A retrofit filter would also decrease the effectiveness of the light shielding, leading to greater light trespass into homes, greater light directed upward into the sky, and greater risk of glare. 

Finally, high heat will damage even the best of filters, decreasing their effectiveness and requiring their replacement, likely much more frequently than the LEDs themselves. 

Overall, then, adding a filter would increase the cost of the lighting by the cost of the filter, its relatively frequent replacement, the higher cost of higher lumen LEDs, the greater electricity cost to drive the higher lumen LEDs, and the costs associated with repair of lights whose warranty has been voided. 

If your goal is a “yellow” light, it will be less costly, much more energy efficient, and much more reliable to purchase a light made to produce that color of light.